1. Field of the Invention
The present invention relates to a film forming system and method for performing a film formation process to process objects such as semiconductor wafers.
2. Description of the Related Act
In general, a vertical heat treatment system, which is advantageous for dust elimination and space saving, is used as a heat treatment system for performing a thermal diffusion process or a film formation process for semiconductor device manufacturing (refer to Japanese patent laid-open publications JP4-269824A and JP2003-282452A, for example).
Such a vertical heat treatment system includes a heat treatment furnace vertically housed in an upper section of a rectangular housing, and having a cylindrical reaction tube made of quartz, and a heater and thermal insulator which are disposed around the reaction tube. A standby space, allowing a wafer boat carrying many semiconductor wafers (i.e., process objects) thereon to stand by, is provided in the housing below the heat treatment furnace. The wafer boat is loaded into and unloaded from the heat treatment furnace by means of a boat elevator. Due to the above structure, the vertical heat treatment system is advantageous for footprint reduction, as compared with a horizontal heat treatment apparatus including a horizontal heat treatment furnace. In addition, in the vertical heat treatment system, the wafer boat can be loaded into and unloaded from the heat treatment furnace without colliding with the reaction tube, and thus the generation of particles can be minimized.
In order to achieve an increased degree of cleanness, the vertical heat treatment system employs a dust elimination filter, through which a clean gas is supplied to the standby space to pass through the entire standby space, thereby preventing particles or dust from adhering to the semiconductor wafers in the standby space. Part of the clean gas passed through the standby space is circulated, while the remaining part of the clean gas is discharged out of the system to an exhaust system.
Recently, a higher degree of cleanness (particle elimination) is required to meet the requirements of a higher degree of miniaturization and integration of semiconductor devices and efficient mass production.
A film formation process forms thin films not only on the semiconductor wafers but also on the entire surface of the wafer boat. The unnecessary thin film formed on the wafer boat surface can be removed by a cleaning process, which is performed every time after the wafer boat is used for the film formation process for a certain times. However, in areas where the wafers contact the wafer boat, the thin film formed on the edge of each wafer is connected to the thin film formed on the wafer boat. Thus, when the wafer is removed from the wafer boat, the connection is broken so that fragments of the thin film exist on the wafer boat surface. The fragments can readily be removed from the wafer boat surface, and are likely to adhere to a subsequently processed wafer to contaminate it with particles originated from the fragments.